2. The cardiac cycle
This presentation goes through the stages of the
cardiac cycle that occur in one full contraction
of the heart.
3. The cardiac cycle
There are four stages of the cardiac cycle:
I. Isovolumetric contraction
II. Ventricular ejection
III. Isovolumetric relaxation
IV. Ventricular filling
4. The cardiac cycle
Broadly the stages of the cardiac cycle can be
divided into systole and diastole:
I. Isovolumetric contraction
Systole- when the ventricles
II. Ventricular ejection are contracting
III. Isovolumetric relaxation
Diastole- when the
IV. Ventricular filling ventricles are relaxing
Here the cycle has been depicted as starting from
the end of diastole when the ventricles are
relaxed and filled with blood
5. Phase 1: Isovolumetric Contraction
The left ventricle is
full of blood and
begins to contract.
This causes the
pressure in the left
ventricle to increase.
6. Phase 1: Isovolumetric Contraction
Once the pressure in
the left ventricle
exceeds that of the
left atrium the mitral
valve will close.
This is to prevent
blood from going
back into the left
atrium.
Mitral valve closes
7. Phase 1: Isovolumetric Contraction
The ventricles
continue to
contract, but until the
aortic valve opens the
pressure in the left
ventricle increases
with no change in
volume- this is
isovolumetric Isovolumetric
contraction. contraction
8. Phase 2: Ventricular ejection
Once the pressure in
the left ventricle
exceeds that of the
aorta the aortic valve
will open.
Aortic valve opens
9. Phase 2: Ventricular ejection
Blood then leaves Ventricular ejection
the left ventricle into
the systemic
circulation via the
aorta- ventricular
ejection
10. Phase 3: Isovolumetric relaxation
The ventricles now Aortic valve closes
begin to relax once
the blood has been
ejected.
When the pressure
in the left ventricle
falls below that of
the aorta the aortic
valve will close. This
prevents blood
flowing back into the
left ventricle from
the aorta.
11. Phase 3: Isovolumetric relaxation
As the ventricles
relax the pressure
will fall, but there
will be no change in
volume until the
mitral valve opens-
this is isovolumetric
Isovolumeteric
relaxation relaxation
12. Phase 4: Ventricular filling
Once the pressure in
the left ventricle falls
below that in the left
atrium the mitral
valve will open.
This then allows the
ventricles to fill with
blood from the left
atrium, preparing Mitral valve opens
the ventricles for
another round of the
cardiac cycle.
13. The cardiac cycle- recap
Phases of the cardiac cycle:
I. Isovolumetric contraction
Systole
II. Ventricular ejection
III. Isovolumetric relaxation
Diastole
IV. Ventricular filling
